The present disclosure relates to a means of fabricating aspheric (non-spherical) mirrors to be used in modern reflective telescopes for either ground- or space-based applications. Reflective telescopes use mirrors to collect and focus light to an image, while refractive telescopes use lenses rather than mirrors. Reflective telescopes generally produce higher quality images than refractive telescopes when used over a wide range of optical wavelengths. They are also considerably lighter than refractive telescopes for large telescope apertures. Many modern ground-based telescopes have apertures that exceed several meters. The Hubble Space Telescope has an aperture of approximately 2.5 meters. Lenses of sufficient optical quality are not available in such large sizes, and their weight would be prohibitive. Therefore, the manufacture of large aspheric mirrors for modern telescopes has been an area of extensive development for several decades.
The fabrication of aspheric mirrors by conventional grinding and polishing techniques is time-consuming and expensive. The reason for this is the fact that an aspheric mirror has a local curvature that varies as a function of position on the mirror. A spherical mirror, on the other hand, has a constant curvature over its entire surface. Grinding and polishing of a spherical mirror can be accomplished by using a large tool that contacts the full aperture of the mirror. With an abrasive substance located between the tool and the mirror, the tool is stroked back-and-forth across the surface of the mirror in order to remove material. The nature of the abrasive material and the pressure used is varied as the mirror shape converges to the desired shape. When an aspheric mirror is ground and polished, however, a large tool cannot be used since it cannot match the mirror's contour as the tool is stroked across the mirror. Consequently, the tool size must be decreased to the point where the mismatch in shape between the mirror and tool is acceptable over the extent of the stroke used. This significantly reduces the rate at which material can be removed from the mirror, adding considerable time, and therefore cost, to the fabrication of the mirror. The subject invention offers a new approach to the fabrication of aspheric mirrors that leverages the fact that spherical mirrors can be efficiently fabricated by conventional means.